The invention was developed in the environment of helicopter rotor blade repair, and will be described primarily in connection with that application. It will be understood by those knowledgeable in the art that the invention may have wider application to aerofoils for other purposes.
A typical helicopter rotor blade has an inboard mounting end including a suitable fitting used to mount the blade on the rotor hub of an aircraft. As understood by skilled persons in the art of rotor blades, an aerofoil portion of the blade typically spans from the inboard end section to the blade tip and includes a flight section and a flex section. The flight section which is farthest from the axis of rotation travels at the greatest speed and provides the majority of the lift. Inboard from the flight section is the flex section which undergoes bending deflection under lift forces exerted on the blade in use. In a conventional rotor blade design the flex section is continuous in profile and formed of similar material as the outboard flight section so as to have similar rigidity. The flex section generally comprises a center spanwise working section of the blade. On conventional blades, a trim tab is typically located at the trailing edge to ensure that the blades track one another. The trim tab is commonly located at a transition point on the blade at which flexing of the blade is substantially reduced in operation, such that the flex section is typically defined as the portion of the blade which spans between the inboard end section and the trim tab.
The leading edges of helicopter rotor blades are subject to environmental wear, particularly when the helicopter is operated in harsh conditions, for example with significant quantities of ambient sand or salt. It has been found in particular that there is a recurring problem of skin erosion located inboard of the metal leading edge abrasion strips in main rotor blades. Current practice is to remove the blades from the helicopter and send them for repair. In some cases, the damage cannot be repaired. The damage requires skin repairs to the leading edge with reinforcement doublers applied. It has been found that a metal skin repair in the flex section of the blade is prone to delamination.
Impact damage is another significant concern with rotor blades since impact damage to the blade also requires removal of the blade and shipping to specialized shop capable of performing the repairs.
Either repair, of erosion or impact damage can mean several weeks downtime for the aircraft while the blade is dismounted, packed and shipped, repaired and returned.
U.S. Pat. No. 4,580,944 to Miller discloses a flexible rotor connector for a rotary wing aircraft in which a flexible aerodynamic foam covering is then applied to this flexible rotor connector. A moisture resistance polyurethane coating is recommended primarily to protect the flexible aerodynamic foam covering from moisture damage. The primary purpose of the flexible rotor connector is to provide a means of attaching the rotor blade component to the helicopter rotor head drive/control systems and therefore does not form a part of the rotor blade component whatsoever. Due to the underlying foam, the rubber coating is clearly not intended to protect against any impacts. The only impact resistant coverings known in the prior art specifically for the leading edge of a rotor blade, involve a metal strip laminated to the leading edge. Miller in particular discloses no form whatsoever of a wear resistant strip on the blade itself.
The present invention is concerned with an alternative arrangement that ameliorates many of the problems with current repair techniques for aerofoil leading edges.